Elevated IOP is clearly the dominant risk factor in glaucoma as the probability of damage to the optic nerve increases with increasing pressures. The IOP, however, is not constant during the day and can have large fluctuations, especially in glaucoma patients. As mentioned in the NEI National Plan and by the Study Section: "We still do not know if it is true average pressure, the occasional peak, or the variation...that is the most important. Nor do we completely understand the spontaneous variations of IOP. Thus home tonometry has much appear." In response to this need, a Self-Tonometer has been developed that can be used by the patient alone, at home or at work, and has been shown to be safe and accurate. The clinical application indicates so far that new and valuable information can be gained by home tonometry. Future studies will address some of the areas in which information is still lacking: 1) The effort in the past has led to the recruitment and beginning of follow-up of primary open angle glaucoma patients with apparently well-controlled IOP and of low tension glaucoma patients. These patients, and additional recruits, will be followed up prospectively by home tonometry, clinical evaluation and stereo disc photography. This will us allow to better characterize the behavior of IOP with time and to assess the predictive value of the parameters of the IOP diurnal variations for the progression of glaucomatous damage. 2) Patients who had surgery following a progression in visual field loss will be followed up after it is determined by, office tonometry, that they have well-controlled IOPs. This will provide information on the nature of the IOP diurnal variations and the curve types following different surgeries (laser trabeculoplasty, partial-thickness and full-thickness filtering surgery); comparison of the degree of long-term normalization of the diurnal IOP variations achieved by the different surgeries versus medical treatment; and assessment of the value of diurnal variation parameters in predicting further progression of glaucoma in this group which is particularly sensitive to further damage. 3) We have detected the presence of significant IOP peaks upon wakening. Self-Tonometry will be performed close to the time of wakening in order to assess the prevalence of early morning peaks in normals, and subjects with low tension glaucoma, open angle glaucoma or ocular hypertension. The presence of such peaks in a significant portion of the population would indicate that home tonometry has a particular diagnostic importance as the only practical method to detect potentially damaging IOPs. 4) Finally, more clinical experience will define the kind of patients needing home tonometry and the benefits that can be expected in diagnosis and management.